Investigators are racing to find definitive answers before the case becomes a new flashpoint in inter-Korean relations and South Korea’s ideological divide.
The blast occurred as troops were opening a route toward an area near the Military Demarcation Line, or MDL, where changes in the terrain had prompted South Korea’s military and the UNC to plan an on-site inspection.
A joint South Korean-UNC team entered the Demilitarized Zone on Sunday, six days after the blast, but could not reach the exact site. The team spent the day searching for mines and extending an access route. About 40 personnel took part in the operation.
Here are four key questions about the accident and the military’s response.
Q1: Why did South Korean troops have to clear a route before the UNC inspection?
The military says no existing route led to the area the UNC wanted to inspect.
South Korean forces detected terrain changes near the MDL and shared information on several locations with the UNC. The command determined that an on-site inspection was needed, according to the Joint Chiefs of Staff.
But the area could not be reached by an established search route.
“It was a new area with no existing search route,” a JCS official said at a Defense Ministry briefing Monday. “Because it had not been accessed for decades, we had no choice but to clear a route.”
The UNC wanted to inspect the area in person, the JCS said, so troops first had to create physical access to it.
“What the UNC requested was to go to the site and see it directly,” the official said. “So clearing a search route had to come first.”
South Korean troops reportedly cleared about 200 meters of new route on the day of the blast. The area was covered with thick vegetation and lay close to the MDL.
The military was aware of the significant risks in the area.
The JCS describes it as an “unverified mine area,” meaning it is not a sector where South Korean troops have operated continuously since the 1953 armistice and where the locations of all possible mines are known.
The military says the area could contain mines laid decades ago, as well as explosives displaced by later changes in terrain or other conditions.
Other risks included the site’s proximity to the MDL, limited visibility through dense vegetation and the difficulty of monitoring some parts of the area directly from South Korean positions. The JCS said it also uses satellite and other imagery where direct surveillance is difficult.
A former South Korean Army noncommissioned officer who served for more than seven years with the 25th Infantry Division, including in a search unit responsible for the sector, told AJP on condition of anonymity that surveillance in the area near the blast site had been interrupted for an extended period.
A nearby guard post was among those withdrawn and dismantled under the 2018 inter-Korean military agreement before being restored years later, the former officer said.
“There was a surveillance gap of roughly five years,” the former officer said. “We cannot know exactly what happened in that area during that period, so that gap also needs to be examined.”
Under the 2018 agreement, South and North Korea each agreed to withdraw 11 guard posts inside the DMZ. Ten were demolished, while one was preserved without troops or weapons. South Korea later restored all 11 positions after the agreement unraveled, completing the work in May 2025.
The JCS said South Korean forces and the UNC had communicated through senior and working-level channels since the day of the blast and had agreed on arrangements for the investigation. It rejected suggestions that a lack of coordination with the UNC alone had delayed the probe.
The military has disclosed few details about the specific risk assessment conducted before the Sept. 21 operation, citing operational security.
The military says there was no existing route to the site.
Asked by AJP whether troops could have reached the area without first entering the unverified mine zone, the JCS said it had not been accessed for decades and that a new route therefore had to be opened.
The military has given less detail about whether unmanned systems were considered.
Asked whether robots or other unmanned equipment could have been used, the JCS said the option had not been discussed separately with the UNC for this operation.
The official said robotic systems are used in some other areas but did not say whether they had been considered and ruled out in this case.
The military had other ways to monitor the broader area, including satellite and other imagery. But the UNC had requested an inspection on the ground.
Remote surveillance could show changes in the terrain, but under the plan adopted by the two sides, troops still had to reach the site in person.
That remains the central unanswered question.
The military has not formally confirmed the type of explosive, though it says a land mine remains the leading possibility.
The JCS said Monday that several personnel reported seeing objects near the blast site resembling a North Korean-style wooden-box mine. Other accounts described material that appeared to be mostly plastic. Officials cautioned against identifying the mine before the site is examined.
Several scenarios remain possible.
The explosive could have been a mine laid decades ago. Because the area has not been regularly accessed since the armistice, the military says mines from the Korean War or later periods cannot be ruled out.
Another possibility is that it was a North Korean mine. The blast occurred only several dozen meters from an area where North Korean troops are suspected of laying mines near or south of the MDL. But proximity alone does not show that North Korea recently placed the mine involved in the blast.
Even if investigators determine that the mine was North Korean, they will still need to establish how and when it reached the site.
A stream runs near the area, raising the possibility that a mine laid elsewhere was carried there by heavy rain or changing terrain. Investigators will also examine whether it was placed there more recently.
The military has sent equipment worn by the injured troops, material containing explosive residue and fragments removed during surgery to the National Forensic Service for analysis. As of Monday, the JCS said it had not received an official forensic result.
Investigators will need evidence from the blast site, including fragments, the mine’s material and explosive composition, its position and the surrounding terrain, to determine what exploded and whether it had been there for decades, was washed into the area or was placed there more recently.
Until then, the military says it is keeping all possibilities open.
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